A tag created by mistake, it doesn’t show on /tags list,
neither in the tags group, even /tags/{tag}
but only appear when you are going to have a new topic,
it’s just right there, couldn’t find any way to let it disappear 
AI-generated summary
ncl reported an issue with deleting a tag that wasn’t assigned to any topics. The tag wouldn’t appear in the /tags list or group, making it difficult to delete. zogstrip suggested adding the tag to a topic, which would allow it to be deleted from the /tags page. This solution worked for ncl. Additionally, zogstrip mentioned a recent commit that now allows staff members to see all tags, making it easier to delete unused ones.
Add the tag to a topic, then it’ll show up in /tags and you’ll be able to delete it.
It works! thank you soooo much!!!
Staff members will now see all the tags (making it easier to delete unused tags) 
https://github.com/discourse/discourse/commit/37232fcb58b552d9ee752f49bf0ce624ba2a82c8